1. Field of the Invention
The present invention relates generally to a display apparatus for an automotive vehicle, in particular to a so-called `head-up` type display apparatus which optically forms virtual image showing information, such as driving information and so forth. More specifically, the invention relates to a head-up display apparatus which can form the virtual image overlapping the front sight of a vehicular driving to avoid necessity of looking down into an vehicular instrument panel for obtaining driving information, such as vehicle speed, engine speed, fuel amount, engine temperature and so forth. 2. Description of the Background Art
Japanese Patent First (unexamined) Publications (Tokkai) Showa Nos. 60-88925 and 60-88926 discloses head-up type display apparatus. The disclosed apparatus employs a semi-transparent image projecting panel arranged inside of a front windshield. Virtual image containing vehicular driving information, such as vehicle speed (speed meter), engine speed (tachometer), fuel amount (fuel gauge), engine coolant temperature (TEMP. gauge) and so forth, is projected on the image projecting panel. The image projecting panel is formed into subatantially flat plane plate.
An optical image source is provided within an instrument panel and is designed to project optical image for forming the virtual image on the image projecting panel through a transparent projector window. The transparent window is sealingly closed by a transparent panel which has upper surface lying in flash to the upper surface of the instrument panel.
In such construction, the transparent panel in the projector window tends to reflect sun beam or shine in the day light to cause drop of contrast of the virtual image formed on the image projecting panel. This degrades visibility of the displayed image.